The present invention is directed to catheters, and particularly to steerable, miniscope catheters.
The use of miniscopes for performing diagnostic testing and for assisting in the performance of certain types of surgery is gaining acceptance in the field of medicine. Miniscopes are advantageously utilized in procedures requiring passage through very small ducts or passageways of the patient. Examples of such procedures include the examination of the bile and pancreatic ducts, with reference being made to "Direct Cholangioscopy and Pancreatoscopy at Time of Endoscopic Retrograde Cholangiopancreatography", Richard A. Kozarek, M.D., The American Journal of Gastroenterology, Vol. 83, No. 1, 1988, pages 55-57, and "Endoscopy of the Gallbladder as Control of Gallstone Therapy with Methyl-tert-Butyl Ether", Leuschner, Helstern, Birkenfeld, Leuschner, Gatzen, Kurtz and Fischer, The American Journal of Gastroenterology, Vol. 83, No. 2, 1988, pages 169-172.
While the use of miniscopes is increasing in diagnostic and surgical procedures, such devices suffer intrinsic disadvantages. Basically a miniscope is a multiple lumen catheter equipped with one or more optical filaments, which filaments may consist of a single fiber or a coherent bundle of optical fibers. The filament is positioned within a selected one of the catheter lumens. The optical filament used in constructing the catheter miniscopes are selected from specific types of optical filament. For example, the catheter miniscope will include at least one optical filament, typically a coherent bundle of glass fibers which possesses sufficient light transmissive properties, and while providing minimal distortion, to function as the view scope. This optical filament has a lens fitted at its distal end, that is the end which will lead the catheter into the body. This lens will be sufficient enough to magnify and focus the viewed object. A viewing eye piece will be secured at the opposite, proximal end of this filament optic. Additional optical filaments can be included for providing illumination. These types of optical filaments need not possess the same optical purity as the optical filament used to function as the viewing filament.
Generally miniscopes must have a relatively narrow diameter in order to allow access into the small conduits for which such devices are intended. For example, miniscope catheters having an outside diameter of seven french or less would be desirable for atraumatic passage into the bite or pancreatic ducts. While catheter miniscopes having this diameter or less have been constructed, such catheter miniscopes do not possess the type of maneuverability required to manipulate the catheter distal end carrying the catheter optics. This is particularly critical when the catheter needs to be moved into a particular duct, which intersects another duct. Specifically, the distal end of the catheter must be deflectable to provide the doctor with sufficient enough control to insert the catheter into the proper duct.
Catheters possessing the desired maneuverability do exist. Such catheters rely upon different techniques for providing the desired maneuverability. Basically, the maneuverability of the catheter is provided by bending the distal tip of the catheter. This allows the catheter to be maneuvered through tortuous passages of the patient's body during a procedure. One type of mechanism for bending the catheter tip involves pre-forming the distal tip to the desired shape of the passage through which the catheter will be positioned. While this is somewhat effective for certain procedures, such types of catheters can not be satisfactorily controlled due to the lack of torque transmission over the length of the catheter body. Another technique involves inserting a stylet into a catheter lumen, with the stylet being preformed. This type of procedure suffers the same disadvantage as preforming the catheter distal end.
An early device for truly controlling the maneuverability of catheter distal ends is taught in U.S. Pat. No. 3,521,620, issued to Cook on July 28, 1970. The taught device is basically a coil spring which is fitted about a wire. This wire is eccentrically secured to the distal end of the coil spring. The wire turnings at the distal end of the coil spring are spatially separated, while the remainder of the coil spring is tightly wound. When the wire is pulled the coil distal end windings become compressed on one side. The eccentric attachment of the wire to the coil distal end causes a bending moment which differentially compresses the coil windings. The result is an off axis deflection of the coil. This device can be inserted into a lumen of a catheter. The off axis deflection of the coil is transmitted to the distal end of the catheter, resulting in a deflection of the catheter distal tip.
A similar approach for controlling the deflection of a catheter distal end is taught in European Patent Applications 176,865, published on Sept. 4, 1986, and 254,885, published on March 2, 1988. The catheters taught in these two published applications cause the distal tip deflection by applying tension to a wire which has been secured eccentrically at the distal end of the catheter.
Other approaches for controlling the deflection of a catheter distal end involve inflating an eccentric catheter balloon, which has been constructed in the distal end. Some catheters may utilize short bursts of gas from out of a side vent to deflect the catheter distal end.
Some techniques involve the construction of the catheter wall at the distal end with portions of differing rigidity, e.g. by varying the thickness of the wall about the catheter circumference. This may also be accomplished by affixing a rigid member along a portion of the catheter wall. When the distal end is subjected to an axial compressive force the rigid portion will not as easily constrict. This results in the catheter bending towards the less rigid, or thinner portion of the side wall. An example of this type of catheter is disclosed in the Patent Cooperation Treaty Patent Application Number WO 87/01600, which was published on March 26, 1987.
While all of the approaches taught by these references provide for adequate control of the distal end deflection, such approaches are unavailable for the catheter miniscope. This is because such catheter miniscopes must possess a relatively small outside diameter, e.g. 2.8 millimeters or less. The methods employed in the above referenced disclosures require more space than is available with catheters of this size, particularly, when such catheters must also include at least one working lumen. The working lumen would have to be provided with a sufficient size to accommodate the passage of guide wires, electrical wiring or fluid. The space availability is also compromised by the fact that such catheter miniscopes will be provided with the necessary optical filaments.
There thus exists the need to construct a catheter miniscope having the necessary optical filaments, while also being designed to provide the necessary maneuverability to deflect the distal end.